http://www.tomshardware.com/reviews/cpu-hierarchy,4312.html
It's 2 tiers higher (which is usually the minimum you want to do), & you not only get 2 more cores but faster cores (base speed goes from 3.5GHz to 4GHz, boost from 4.1 to 4.2).
However, you have to make sure that your board can handle it. Some of the AM3+ boards are limited to the 95W CPUs (like your current FX-6300). Unfortunately, all of the 8-core FX chips in that category (FX-8300, FX-8320E, & FX-8370E) are at the same tier as your current CPU -- mainly because even with the extra cores & faster turbo speeds their base core speeds are slower.
If you're comfortable with OC'ing your system, getting a decent ($30-50 USD) air-based aftermarket cooler would allow you to ramp up your current chip for some better performance, while allowing you save up for a future system next year (i.e. once Zen is available & can be compared to Intel's offerings). If you're not as comfortable with OC'ing your system
and your board can handle one of the 125W chips, then definitely get an FX-8350 (or even the FX-8370, as its boost speed is slightly higher).